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<h3>Apache HTTP Server Version 1.3</h3>
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<h1 align="CENTER">Hints on Running a High-Performance Web
Server</h1>
Running Apache on a heavily loaded web server, one often
encounters problems related to the machine and OS
configuration. "Heavy" is relative, of course - but if you are
seeing more than a couple hits per second on a sustained basis
you should consult the pointers on this page. In general the
suggestions involve how to tune your kernel for the heavier TCP
load, hardware/software conflicts that arise, <em>etc.</em>
<ul>
<li><a href="#AUX">A/UX (Apple's UNIX)</a></li>
<li><a href="#BSD">BSD-based (BSDI, FreeBSD, etc)</a></li>
<li><a href="#DEC">Digital UNIX</a></li>
<li><a href="perf-hp.html">HPUX</a></li>
<li><a href="#Linux">Linux</a></li>
<li><a href="#Solaris">Solaris</a></li>
<li><a href="#SunOS">SunOS 4.x</a></li>
<li><a href="#SVR4">SVR4</a></li>
</ul>
<hr />
<h3><a id="AUX" name="AUX">A/UX (Apple's UNIX)</a></h3>
If you are running Apache on A/UX, a page that gives some
helpful performance hints (concerning the <em>listen()</em>
queue and using virtual hosts) <a
href="http://www.jaguNET.com/apache.html">can be found here</a>
<hr />
<h3><a id="BSD" name="BSD">BSD-based (BSDI, FreeBSD,
etc)</a></h3>
<a href="perf-bsd44.html#initial">Quick</a> and <a
href="perf-bsd44.html#detail">detailed</a> performance tuning
hints for BSD-derived systems. <a
href="perf-bsd44.html#accf">Accept filtering</a> on FreeBSD.
<hr />
<h3><a id="DEC" name="DEC">Digital UNIX</a></h3>
<ul>
<li><a
href="http://www.digital.com/info/internet/document/ias/tuning.html">
DIGITAL UNIX Tuning Parameters for Web Servers</a></li>
<li>We have some <a href="perf-dec.html">newsgroup
postings</a> on how to tune Digital UNIX 3.2 and 4.0.</li>
</ul>
<hr />
<h3><a id="Linux" name="Linux">Linux</a></h3>
There are no known problems with heavily loaded systems running
Linux kernels 2.0.32 or later. Earlier kernels have some
problems, and an upgrade to the latest 2.0.x is a good idea to
eliminate various security and denial of service attacks.
<hr />
<h3><a id="Solaris" name="Solaris">Solaris 2.4</a></h3>
The Solaris 2.4 TCP implementation has a few inherent
limitations that only became apparent under heavy loads. This
has been fixed to some extent in 2.5 (and completely revamped
in 2.6), but for now consult the following URL for tips on how
to expand the capabilities if you are finding slowdowns and
lags are hurting performance.
<p>Other links:</p>
<ul>
<li><a
href="http://www.sun.com/sun-on-net/performance.html">World
Wide Web Server Performance,
<http://www.sun.com/sun-on-net/performance.html></a></li>
<li><a
href="http://www.rvs.uni-hannover.de/people/voeckler/tune/EN/tune.html">
Solaris 2.x - tuning your TCP/IP stack</a> contains some good
technical information about tuning various Solaris TCP/IP
parameters.</li>
</ul>
<hr />
<h3><a id="SunOS" name="SunOS">SunOS 4.x</a></h3>
More information on tuning SOMAXCONN on SunOS can be found at
<a
href="http://www.islandnet.com/~mark/somaxconn.html">http://www.islandnet.com/~mark/somaxconn.html</a>.
<hr />
<h3><a id="SVR4" name="SVR4">SVR4</a></h3>
Some SVR4 versions waste three system calls on every
<samp>gettimeofday()</samp> call. Depending on the syntactic
form of the <samp>TZ</samp> environment variable, these systems
have several different algorithms to determine the local time
zone (presumably <em>compatible</em> with something). The
following example uses the central european time zone to
demonstrate this:
<dl>
<dt><strong>TZ=:MET</strong></dt>
<dd>
This form delegates the knowledge of the time zone
information to an external compiled zoneinfo file (à
la BSD).<br />
<strong>Caveat:</strong> Each time the gettimeofday()
function is called, the external zone info is read in again
(at least on some SVR4 systems). That results in three
wasted system calls with every apache request served.
<pre>
open("/usr/lib/locale/TZ/MET", O_RDONLY) = 3
read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 7944) = 778
close(3) = 0
</pre>
</dd>
<dt>
<strong>TZ=MET-1MDT,M3.5.0/02:00:00,M10.5.0/03:00:00</strong></dt>
<dd>This syntax form (à la SYSV) contains all the
knowledge about time zone beginning and ending times in its
external representation. It has to be parsed each time it is
evaluated, resulting in a slight computing overhead, but it
requires no system call. Though the table lookup à la
BSD is the more sophisticated technical solution, the bad
SVR4 implementation makes this the preferred syntax on
systems which otherwise access the external zone info file
repeatedly.</dd>
</dl>
You should use the <samp>truss</samp> utility on a
single-process apache server (started with the <samp>-X</samp>
debugging switch) to determine whether your system can profit
from the second form of the <samp>TZ</samp> environment
variable. If it does, you could integrate the setting of the
preferred <samp>TZ</samp> syntax into the httpd startup script,
which is usually simply a copy of (or symbolic link to) the
<samp>apachectl</samp> utility script, or into the system's
<samp>/etc/TIMEZONE</samp> script.
<hr />
<h3>More welcome!</h3>
If you have tips to contribute, send mail to <a
href="mailto:apache@apache.org">apache@apache.org</a>
<hr />
<h3 align="CENTER">Apache HTTP Server Version 1.3</h3>
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